1. Field of the Invention
This invention relates to a portable apparatus for testing and observing chemical interactions of a fluid sample, and a process for testing fracturing fluids commonly used for oil reservoir and/or water shutoff treatments.
2. Description of Related Art
Hydraulic fracturing, including introduction of proppants in subterranean oil-bearing reservoir rock formations, is a well known procedure to stimulate well production. Typically, the fracturing fluid and proppants are mixed in a mobile storage vessel, e.g., a trailer-mounted fluid storage container known as a “frac-tank,” located at the surface near the well site. Chemical additives, including gel polymers and chemical inhibitors, and energizing components such as carbon dioxide and nitrogen gas, are also mixed in the fracturing composition.
After adequate mixing in the frac-tank, the fracturing fluid is pumped via high-pressure lines through the wellhead and down the wellbore. During ideal hydraulic fracturing operations, the fluid passes into the reservoir formation and induces fractures, and petroleum liquid and gas movement from the reservoir rock into the wellbore is increased, thereby enhancing the recovery of hydrocarbons.
Typically, a viscous, surface-mixed stimulation fluid mixture is injected at pressures adequate to create and propagate fractures in the reservoir. The pressures required to pump such stimulation treatments are relatively high, particularly during injection of gelled, thickened fluids that often are used to propel proppant into the fractures. These pumping pressures will often increase during the treatment process.
Furthermore, in order to effectively transport proppant, use of high viscosity gelling compositions is desirable. However, if viscous gelling occurs prematurely, e.g., in the tanks and/or flowlines or otherwise before the fluid is pumped in the well, the fluid introduction rates decrease and excess pressures are encountered. Various chemical inhibitors, such as encapsulated or chemically coated inhibitors, can be mixed into the fluid mixture to provide a time-delayed gelling of the fracturing fluid in order to avoid premature gelling. Other known additives can also be incorporated for the purpose of controlling the gelling rate. For instance, inhibitors to time-delay activation of cross linked polymer gels can be included.
Many stimulation operations are not ideal due to various problems, including limitations associated with mixing of the stimulation fluid and incompatible chemical mixtures. Selection of the appropriate formulation for a fracturing fluid for a given field operation is conventionally a trial-and-error process. In the event that the frac chemicals are not performing properly, premature termination of the fracturing operation is required to prevent conditions dangerous to the personnel and equipment failures such as rupturing of the wellbore casing and other components in hydraulic communication with the fluid source. A premature termination incurs substantial costs and lost time.
In order to minimize the problems associated with conventional hydraulic fracturing operations, quality control and quality assurance analyses are conducted prior to introducing the fracturing composition downhole. Various defects in the frac fluid can be ascertained in these quality control and quality assurance analyses. For instance, the frac tank itself may be contaminated, causing undesirable side reactions of the frac fluid. In other undesirable situations, the frac fluid composition and/or mixture is not what was originally intended, e.g., due to human error in the field.
In actual frac operations at a well site, major equipment and associated potential problems are usually considered, including standby pump trucks and standby blenders. However, quality control programs are desirable because unexpected problems can arise, which are generally much less obvious, and, while they may not terminate the treatment, these problems can ultimately compromise the efficacy of the fracturing operation.
While vendors of frac fluids and their various additives have a working knowledge of most chemical interactions, additive incompatibility nonetheless remains a problem in the industry. For instance, one or more additives may be incompatible with the fracturing fluid, the energizing component, and/or the breaking agents under the prevailing well conditions, i.e., the high temperatures and pressures under which well stimulation occurs.
Quality assurance is undertaken to identify potential problem areas and eliminate them before any problem arises. While many quality assurance and quality control programs rely on various forms and checklists which document the equipment, inventory and instrumentation available on location and after the treatment, materials used and personnel performance, the industry lacks reliable apparatus and a comprehensive protocol to accommodate the requisite testing that is required and which is preferably performed at the drilling site shortly before the frac operation is scheduled to begin.
While many tests can be performed in a laboratory setting, often the actual fluids utilized in the field can differ from the chemicals used in a controlled laboratory environment. For instance, while the aqueous fracturing fluid tested in the laboratory can be supplied directly from the vendor, fracturing fluid use in the field has been sitting in a frac tank and can become contaminated. The quality of the source water can also differ between the field and the laboratory. In addition, the chemicals, additives and other fluids used in the field can be from different product batches than those tested in the laboratory.
Historically, there is been hesitation to conduct actual on-site testing of the frac fluids due to inadequate time and resources to conduct comprehensive tests for each operation. At a minimum, it is desirable to test base fluid properties including viscosity, temperature and pH. It can also be desirable to conduct crosslink time tests. Other tests that can be conducted at the well site include static break tests and time-temperature viscosity profiles. However, these tests may not always accurately approximate the chemical interactions between the various constituents of the frac fluid under the pressure and temperature conditions to which they will be exposed downhole. The lack of actual on-site testing of the frac fluids can result in significant problems in the event that there is a defect in the frac fluid, e.g., contamination of the frac tank, or the frac fluid composition and/or mixture is not what was originally intended, e.g., due to human error in the field.
U.S. Pat. Nos. 5,018,396, 5,275,063, 4,304,122 and 2,618,151 disclose assemblies for testing permeability of materials in simulated environments, including pressure and temperature conditions. However, these assemblies do not solve the problems related to a lack of actual on-site testing of the frac fluids.
Therefore, it is an object of the present invention to provide an apparatus and process for quality control and quality assurance on-site testing of a frac fluid.
It is another object of the present invention to provide such an apparatus that is easily portable and versatile in use.